allow some ObjectHolder subclasses to continue to be generic

ExternalProgram and CustomTarget have some use cases for producing
subclassed interpreter holders with more specific types and methods. In
order for those subclasses to properly refer to their held_object, we
need a shared base class that is still generic, though bound.

For the derived held objects, inherit from the base class and specify
the final types as the module-specific type.

mesonbuild/interpreter/interpreterobjects.py

@@ -559,8 +559,10 @@ class DependencyHolder(ObjectHolder[Dependency]):
         new_dep = self.held_object.generate_link_whole_dependency()
         return new_dep
 
-class ExternalProgramHolder(ObjectHolder[ExternalProgram]):
-    def __init__(self, ep: ExternalProgram, interpreter: 'Interpreter') -> None:
+_EXTPROG = T.TypeVar('_EXTPROG', bound=ExternalProgram)
+
+class _ExternalProgramHolder(ObjectHolder[_EXTPROG]):
+    def __init__(self, ep: _EXTPROG, interpreter: 'Interpreter') -> None:
         super().__init__(ep, interpreter)
         self.methods.update({'found': self.found_method,
                              'path': self.path_method,
@@ -606,6 +608,9 @@ class ExternalProgramHolder(ObjectHolder[ExternalProgram]):
     def found(self) -> bool:
         return self.held_object.found()
 
+class ExternalProgramHolder(_ExternalProgramHolder[ExternalProgram]):
+    pass
+
 class ExternalLibraryHolder(ObjectHolder[ExternalLibrary]):
     def __init__(self, el: ExternalLibrary, interpreter: 'Interpreter'):
         super().__init__(el, interpreter)
@@ -969,8 +974,10 @@ class CustomTargetIndexHolder(ObjectHolder[build.CustomTargetIndex]):
         assert self.interpreter.backend is not None
         return self.interpreter.backend.get_target_filename_abs(self.held_object)
 
-class CustomTargetHolder(ObjectHolder[build.CustomTarget]):
-    def __init__(self, target: 'build.CustomTarget', interp: 'Interpreter'):
+_CT = T.TypeVar('_CT', bound=build.CustomTarget)
+
+class _CustomTargetHolder(ObjectHolder[_CT]):
+    def __init__(self, target: _CT, interp: 'Interpreter'):
         super().__init__(target, interp)
         self.methods.update({'full_path': self.full_path_method,
                              'to_list': self.to_list_method,
@@ -1007,6 +1014,9 @@ class CustomTargetHolder(ObjectHolder[build.CustomTarget]):
         except IndexError:
             raise InvalidArguments(f'Index {other} out of bounds of custom target {self.held_object.name} output of size {len(self.held_object)}.')
 
+class CustomTargetHolder(_CustomTargetHolder[build.CustomTarget]):
+    pass
+
 class RunTargetHolder(ObjectHolder[build.RunTarget]):
     pass
 

mesonbuild/modules/hotdoc.py

@@ -28,7 +28,7 @@ from ..interpreterbase import (
     InvalidArguments, noPosargs, noKwargs, typed_kwargs, FeatureDeprecated,
     ContainerTypeInfo, KwargInfo, typed_pos_args
 )
-from ..interpreter import CustomTargetHolder
+from ..interpreter.interpreterobjects import _CustomTargetHolder
 from ..interpreter.type_checking import NoneType
 from ..programs import ExternalProgram
 
@@ -364,8 +364,8 @@ class HotdocTargetBuilder:
         return (target, install_script)
 
 
-class HotdocTargetHolder(CustomTargetHolder):
-    def __init__(self, target, interp):
+class HotdocTargetHolder(_CustomTargetHolder['HotdocTarget']):
+    def __init__(self, target: HotdocTarget, interp):
         super().__init__(target, interp)
         self.methods.update({'config_path': self.config_path_method})
 

mesonbuild/modules/python.py

@@ -24,8 +24,8 @@ from ..build import known_shmod_kwargs, CustomTarget, CustomTargetIndex, BuildTa
 from ..dependencies import NotFoundDependency
 from ..dependencies.detect import get_dep_identifier, find_external_dependency
 from ..dependencies.python import BasicPythonExternalProgram, python_factory, _PythonDependencyBase
-from ..interpreter import ExternalProgramHolder, extract_required_kwarg, permitted_dependency_kwargs
-from ..interpreter import primitives as P_OBJ
+from ..interpreter import extract_required_kwarg, permitted_dependency_kwargs, primitives as P_OBJ
+from ..interpreter.interpreterobjects import _ExternalProgramHolder
 from ..interpreter.type_checking import NoneType, PRESERVE_PATH_KW, SHARED_MOD_KWS
 from ..interpreterbase import (
     noPosargs, noKwargs, permittedKwargs, ContainerTypeInfo,
@@ -114,9 +114,9 @@ _PURE_KW = KwargInfo('pure', (bool, NoneType))
 _SUBDIR_KW = KwargInfo('subdir', str, default='')
 _DEFAULTABLE_SUBDIR_KW = KwargInfo('subdir', (str, NoneType))
 
-class PythonInstallation(ExternalProgramHolder):
+class PythonInstallation(_ExternalProgramHolder['PythonExternalProgram']):
     def __init__(self, python: 'PythonExternalProgram', interpreter: 'Interpreter'):
-        ExternalProgramHolder.__init__(self, python, interpreter)
+        _ExternalProgramHolder.__init__(self, python, interpreter)
         info = python.info
         prefix = self.interpreter.environment.coredata.get_option(mesonlib.OptionKey('prefix'))
         assert isinstance(prefix, str), 'for mypy'